Tester for pressure sensors

ABSTRACT

The invention relates to a tester for pressure sensors ( 1 ) in the wafer compound or isolated pressure sensors having a recess for the pressure sensors as well as means for electrical contacting ( 7 ) of the electrical connections of at least one of the pressure sensors. The invention is intended to make it possible to test pressure sensors still in a wafer compound for their function. According to the invention, a pressure head ( 9 ) is provided which has an interior space ( 10 ) open on one side, the open face ( 11 ) of which is capable of being mounted on the pressure sensor ( 1 ) in such a way that the interior space ( 10 ) is tightly sealed by the latter. In this way a static or dynamic pressure of specified amount and duration can be exerted on the sensor element ( 4 ) at least so that the sensor element ( 4 ) is moved out of its resting position. At the same time, the electrical connections ( 7 ) of the selected pressure sensor ( 1 ) are connected with an electrical evaluation unit ( 21 ).

[0001] The invention relates to a tester for pressure sensors in a wafer compound or for isolated pressure sensors as well as for isolated open pressure sensors having a recess for the pressure sensors as well as means for electrical contacting (7) of the electrical connections of at least one of the pressure sensors.

[0002] Pressure sensors on a micromechanical basis contain a pressure-sensitive element that, upon the application of pressure, is at least partially slightly deflected from its resting position and as a result of this deflection/bending indicates a change in electrical voltage similar to a piezoelectric structural element. This change in electrical voltage is amplified by a corresponding evaluation circuit and is largely proportional to the compressive load. Such pressure sensors are commonly produced by semiconductor technology in a wafer compound and have for example a sensor chamber etched into the silicon substrate, one side of which is designed as a diaphragm or sensor element, and which are provided with an aperture or a sensor intake facing this sensor element. In addition, electrical connections for the power supply and the reading of the measured values are found on one side of the pressure sensor, while logic circuits and/or amplifying circuits may additionally be incorporated.

[0003] After completion of the pressure sensors in a wafer compound, they are separated by abrasive cutting into individual pressure sensors/chips, which then for example are finally assembled in housings. This final assembly is then followed by functional testing and, if necessary, calibration of the amplifier circuit to the pressure sensor, while defective pressure sensors are removed.

[0004] It is apparent that the fabrication of pressure sensors requires a considerable expenditure and that it is especially disadvantageous that functional testing of pressure sensors is only done in the completed state.

[0005] The object of the invention therefore is to procure a tester for pressure sensors with which it is possible to test pressure sensors not yet finally assembled and pressure sensors that are still in the wafer compound as well as isolated open pressure sensors for their function and with which it is in particular possible to accommodate the functional characteristics of the pressure sensors.

[0006] The object on which the invention is based is accomplished in a tester of the type mentioned at the beginning in that a means is provided by which a static or dynamic pressure of a specified amount and duration is capable of being exerted on the sensor element of at least one selected pressure sensor so that its sensor element is moved out of its resting position, and in that at the same time the electrical connections of the selected pressure sensor are connected with an electrical evaluation unit.

[0007] A first preferred embodiment of the invention is characterized in that the means is designed as a pressure chamber for production of a static pressure, in which the tester is wholly or partially arranged with the pressure sensors located in a recess. There, at least the selected pressure sensors should be arranged within the pressure chamber.

[0008] A second preferred embodiment of the invention is characterized in that a pressure head is provided which has an interior space open on one side, the open face of which is capable of being mounted on the selected pressure sensor in such a way that the interior space is tightly sealed by the latter. When the tight seal has been obtained, the desired internal pressure can then be built up, including for example stepwise, and the varying electrical measured variables on the electric contacts read.

[0009] This makes it possible to select each of the pressure sensors in the wafer compound successively and mount it on the pressure head accordingly. However, this design makes it alternatively possible to test individual pressure sensors dissolved out of the wafer compound or even partially assembled pressure sensors for their function.

[0010] In addition, the pressure head is connected with a means for production of a specified pressure in the interior space of the same.

[0011] For the control of internal pressure, a pressure-measuring probe is located in the interior space of the pressure head.

[0012] In an additional embodiment of the invention, a means for electrical contacting of the electrical connections of the pressure sensor is assigned to the pressure head. This electrical contacting may be effected by needle probes provided in the interior space of the pressure head. This is of advantage when the electrical connections are arranged on the upper surface of the pressure sensor.

[0013] Since the electrical connections may alternatively be provided at a different location on the pressure sensor, another embodiment of the invention is characterized in that the means for electrical contacting of the electrical connections of the pressure sensor and the pressure head are positionable independently of one another on or under the selected pressure sensor.

[0014] In order to obtain a sufficient seal between the pressure head and the pressure sensor, in another embodiment of the invention it is provided that the pressure head is capable of being mounted on the pressure sensor with a specified compressive force, where the compressive force is produced by a weight or elastic force.

[0015] There the face of the pressure head may be designed as a sealing surface, or a sealing element inserted in the face is provided.

[0016] The compressive force required for a sufficient seal may alternatively be produced by suction with vacuum. To this end, a vacuum groove that is connected with a vacuum-producing means, is incorporated in the face of the pressure head.

[0017] A third preferred embodiment of the invention is characterized in that a thermochuck is provided for the accommodation of pressure sensors located in the wafer compound, where the wafer is arranged face down on the thermochuck in such a way that the sensor intakes of the pressure sensors, arranged in a grid, rest directly on the thermochuck, in that the thermochuck is provided with a grid of holes, and in that the grid of the sensor intakes matches the grid of the holes.

[0018] This embodiment of the invention is provided for pressure sensors in which the electrical connections lie on the back, i.e., are arranged on the side that faces the sensor element.

[0019] In order to ensure sufficient adhesive force on the thermochuck during the application of pressure to individual pressure sensors, the holes in the thermochuck are selectively individually connectable with a means for production of a positive pressure or with a means for production of a negative pressure. i.e., if a positive pressure is produced in a hole, then adjacent holes must simultaneously be impacted by a negative pressure.

[0020] In order to reduce the expenditure for control of the holes, a preferred refinement of the invention is characterized in that the holes are capable of being acted on by pressure, groupwise or alternatively linewise, and the holes adjacent to the selected group or line are capable of being acted on by negative pressure, groupwise or linewise. For electrical contacting, it may be provided in this case that in each instance all pressure sensors of a selected line are electrically contacted simultaneously, so that simultaneous evaluation of the test results is possible.

[0021] A fourth preferred embodiment of the invention is characterized in that a pressure head for production of a flow in the direction of a sensor intake or a sensor element of a selected pressure sensor for production of a dynamic stagnation pressure is provided. This embodiment of the invention, universally applicable per se, is especially suitable for pressure sensors that have a particularly sensitive or uneven surface structure since, in contrast to the other embodiments of the invention, it is not necessary here for the pressure head to be mounted on the pressure sensor. Hence, the risk of any mechanical damage is avoided.

[0022] The pressure head is equipped with a vertically aligned tubule whose lower opening in working position ends at a specified distance above the pressure sensor and whose other end is connected with a pressure-measuring chamber and a test pressure supply line.

[0023] Since the pressure head must in any case be positioned over each selected sensor element, a further development of the invention is characterized in that, at the tubule in the region of its lower opening, a plurality of needle probes are provided for electrical contacting of the electrical connections of the pressure sensor, the needle probes being capable of being mounted on the electrical connections of the pressure sensor in the elastic region.

[0024] In addition, it is alternatively possible to provide an ordinary test card for electrical contacting of each selected pressure sensor and a pressure head which is positionable on the selected pressure sensor independently of the test card.

[0025] In another variant of the invention, a test card for electrical contacting of each selected pressure sensor is provided, a pressure head being positionable on the selected pressure sensor jointly with the test card.

[0026] The pressure head for production of a static pressure, as well as the pressure head for production of a dynamic stagnation pressure, may be fastened to an X-Y-Z cross table.

[0027] The invention will be explained in detail below by means of examples. In the accompanying drawings,

[0028]FIG. 1 shows an embodiment of the invention with a pressure head for production of static pressure in a pressure sensor;

[0029]FIG. 2, another embodiment of the invention according to FIG. 1, but with inside probes for electrical contacting of the pressure sensor;

[0030]FIG. 3, a pressure head with a sealing element arranged on the face, for tight mounting on a pressure sensor;

[0031]FIG. 4, a pressure head with a vacuum groove incorporated in the face for tight fastening of the pressure sensor on a pressure sensor;

[0032]FIG. 5, another embodiment of the invention with a pressure head for production of dynamic pressure; and

[0033]FIG. 6, a schematic representation of an additional embodiment of the invention, wherein the pressure sensors located in a wafer compound on a thermochuck are exposed groupwise to a specified pressure and at the same time vacuum suction is applied to the thermochuck.

[0034]FIG. 1 shows a micromechanical pressure sensor 1 that is still in the compound of a wafer 2, the adjacent pressure sensors not being represented. This wafer 2 is fastened to an ordinary thermochuck 3, where a simple chuck may of course alternatively be used.

[0035] The pressure sensor 1 contains a sensor element 4, which delimits an interior sensor space 5 on one side. A sensor intake 6 is located on the side of the pressure sensor 1 facing the sensor element 4. The pressure sensor 1 may be connected via this intake 6 with another delimited space whose internal pressure is to be determined. In addition, an integrated circuit is provided in the region of the sensor intake 6 for evaluation [of the] amplification of the voltage change produced by the sensor element 4. The power supply of the pressure sensor 1 and the reading of the measured values are provided via electrical connections 7, which in the example represented are arranged on the upper surface of the pressure sensor 1.

[0036] Ordinary test cards, as used in commercially available wafer testers, may be employed for contacting of the electrical connections 7. For electrical contacting the needle probes 8 of the test card simply have to be mounted on the electrical connections 7 and connected at the other end to an electrical evaluation unit. Subsequently, or at the same time, a specified internal pressure must then be produced in the pressure sensor 1. For this purpose, there is provided a pressure head 9, which has an interior space 10 open at one side, the open face 11 of which according to FIG. 1 is mounted on the selected pressure sensor 1 in such a way that its interior sensor space 5 is tightly sealed. At the same time, a weight or elastic force is exerted on the pressure head 9. When the tight seal has been obtained, the desired internal pressure may then be built up, including for example stepwise, and the varying electrical measured variables read at the electrical connections 7. For this purpose, the pressure head 9 is connected with a means for production of the specified internal pressure. A pressure-measuring probe 12, which extends into the interior space 5 of the sensor, is provided for exact determination of the internal pressure obtained in the interior sensor space 5 in each instance.

[0037] If the pressure head 9 is fastened to an X-Y-Z cross table, the possibility exists of successively selecting each of the pressure sensors 1 in the wafer compound and mounting the pressure head 9 on the corresponding pressure sensor 1. It does not matter whether pressure sensors 1 located in a wafer compound or alternatively isolated pressure sensors 1 dissolved out of the wafer compound or alternatively partially assembled pressure sensors 1 are to be selected.

[0038] In addition, the possibility exists of fastening the pressure head 9 directly to the test card and positioning it together with the latter above each pressure sensor 1 selected. It is alternatively possible to fasten the needle probes 8 directly to the pressure head 9.

[0039] At the same time, the dimensions of the pressure head 9 must be selected in such a way that the electrical connections 7 remain free, so that they are freely accessible to the probes 8.

[0040]FIG. 2 shows a variant of the pressure head 9, wherein an enlarged interior space 10 is provided so that the needle probes required for electrical contacting can be arranged in this interior space. Otherwise, there are no other differences from the embodiment of FIG. 1.

[0041]FIGS. 3 and 4 show designs of the pressure head 9 according to the embodiment of FIG. 2. In the design of FIG. 3, a sealing element 13 is provided in the face 11 of the pressure head 9, which element offers the advantage that the required seal is obtained with fairly small weights or elastic forces. Surface damage of the pressure sensor 1 is thus precluded.

[0042]FIG. 4 shows a variant of the pressure head 9, wherein the required pressure force of the pressure head 9 is produced by vacuum suction. For this purpose, a vacuum groove 14 is incorporated in the face 11 of the pressure head 9, which groove is connected with a means for production of a negative pressure.

[0043] It is of course alternatively possible to provide the embodiments of FIGS. 3 and 4 with a pressure head 1 of FIG. 1 and, alternatively, to combine the two embodiments with one another.

[0044]FIG. 5 shows a special embodiment of the invention wherein the required pressure is produced dynamically by a stagnation pressure. To this end, a pressure head 15 is provided for production of a flow in the direction of the sensor intake 6 or of a sensor element of a selected pressure sensor 1 for production of a stagnation pressure. To this end, the pressure head 15 is provided with a vertically aligned tubule 16, whose lower opening 17 ends at a specified distance above the pressure sensor 1 and whose other end is connected to a pressure-measuring chamber 18 and via a throttle 19 to a pressure regulator 20 for a test pressure supply line. Hence, a contactless measurement can be made with the pressure head 15. As already described, here the pressure sensor 1 is likewise fastened to a thermochuck 3.

[0045] The pressure regulator 20 and the pressure-measuring chamber 18 for determination of the actual pressure on or in the pressure sensor 1 are connected to an electrical drive and evaluation unit 21.

[0046] In addition, a plurality of needle probes 22 are provided on the tubule 16 in the region of the lower opening 17 for electrical contacting of the electrical connections 7 of the pressure sensor 1, which probes are capable of being mounted as usual in the elastic region on the pressure sensor 1.

[0047] Alternatively, a test card may be provided for electrical contacting of the electrical connections 7 of each selected pressure sensor 1, the pressure head 15 being positionable independently of the test card or together with the latter on the selected pressure sensor 1.

[0048] In either case, the needle probes 22 on the tubule or the needle probes of the test card have to be connected with the electrical drive and evaluation unit 21.

[0049] Lastly, FIG. 6 shows an embodiment of the invention that is suitable for pressure sensors in which the sensor intakes 6 are arranged on one side of the pressure sensor 1 and the electrical connections 7 are arranged on the opposite side.

[0050] For such pressure sensors, a thermochuck 23 is provided for the accommodation of pressure sensors 1 located in the wafer compound, which is provided with a grid of holes 24 that matches the grid of the sensor intakes 6 of the pressure sensors 1 in the wafer compound.

[0051] Here, the wafer 2 is arranged face down on the thermochuck 23 in such a way that each sensor intake 6 of a pressure sensor 1 faces a hole 24 in the thermochuck 23. This requires that the grid of sensor intakes 6 exactly match the grid of the holes 24 in the thermochuck 23.

[0052] In order to be able to apply pressure on the pressure sensors 1, the holes 24 in the thermochuck 23 are connected individually, groupwise or alternatively linewise with a control box 25. The holes 24 are selectively connectable through the control box 25 with a means for production of a positive pressure or with a means for production of a negative pressure.

[0053] Measurement of the pressure sensors 1 of a selected line is effected in such a way that the corresponding line of the holes 24 in the thermochuck 23 are supplied with a positive pressure and the respective adjacent lines with a negative pressure, in order to ensure that the pressure sensors 1 are held securely on the thermochuck 23.

[0054] Electrical drive of the control box 25 is effected by an electrical control circuit 26 and a multiplexer 27, and evaluation and storage of the test results may then be effected with an ordinary computer 28.

[0055] In all embodiments of the invention, air is preferably used as medium for production of static pressure or of stagnation pressure. In principle, however, it is alternatively possible to use special gases, e.g., nitrogen, or alternatively fluids, for this purpose.

[0056] List of Reference Numerals

[0057]1 pressure sensor

[0058]2 wafer

[0059]3 thermochuck

[0060]4 sensor element

[0061]5 interior sensor space

[0062]6 sensor intake

[0063]7 electrical connection

[0064]8 needle probes

[0065]9 pressure head

[0066]10 interior space

[0067]11 face

[0068]12 pressure-measuring probe

[0069]13 sealing element

[0070]14 vacuum groove

[0071]15 pressure head

[0072]16 tubule

[0073]17 opening

[0074]18 pressure-measuring chamber

[0075]19 throttle

[0076]20 pressure regulator

[0077]21 drive and evaluation electronics

[0078]22 needle probe

[0079]23 thermochuck

[0080]24 hole

[0081]25 control box

[0082]26 drive circuit

[0083]27 multiplexer

[0084]28 computer 

1. Tester for pressure sensors in a wafer compound or for isolated pressure sensors having a recess for the pressure sensors as well as means for electrical contacting of the electrical connections of at least one of the pressure sensors, characterized in that a means is provided by which a static or dynamic pressure of a specified amount and duration is capable of being exerted on the sensor element (4) of at least one selected pressure sensor (1) so that the sensor element (4) is moved out of its resting position, and in that at the same time the electrical connections (7) of the selected pressure sensor (1) are connected with an electrical evaluation unit (21).
 2. Tester according to claim 1, characterized in that the means is designed as a pressure chamber for production of a static pressure, in which the tester is wholly or partially arranged with the pressure sensors (1) located on the recess.
 3. Tester according to claim 2, characterized in that at least the selected pressure sensors (1) are arranged within the pressure chamber.
 4. Tester according to claim 1, characterized in that a pressure head (9) is provided which has an interior space (10) open on one side, the open face (11) of which is capable of being mounted on the pressure sensor (1) in such a way that the interior space (10) is tightly sealed by the latter.
 5. Tester according to claim 4, characterized in that the pressure head (9) is connected with a means for production of a specified pressure in the interior space (10) of the same.
 6. Tester according to claims 4 and 5, characterized in that a pressure-measuring probe (12) is arranged in the interior space of the pressure head (9).
 7. Tester according to any one of claims 4 to 6, characterized in that a means for electrical contacting of the electrical connections (7) of the pressure sensor (1) is assigned to the pressure head (9).
 8. Tester according to claim 7, characterized in that needle probes (8) for electrical contacting of the electrical connections (7) of the pressure sensor (1) are arranged in the interior space of the pressure head (9).
 9. Tester according to any one of claims 1 to 7, characterized in that the means for electrical contacting of the electrical connections (7) of the pressure sensor (1) and the pressure head (9) are positionable independently of one another on or under the selected pressure sensor (1).
 10. Tester according to any one of claims 4 to 9, characterized in that the pressure head (9) is capable of being mounted on the pressure sensor (1) with a specified compressive force.
 11. Tester according to claim 10, characterized in that the compressive force is produced by a weight or elastic force.
 12. Tester according to any one of claims 4 to 11, characterized in that the face (11) is designed as a sealing face.
 13. Tester according to any one of claims 4 to 12, characterized in that a sealing element (13) is inserted in the face (11).
 14. Tester according to any one of claims 4 to 12, characterized in that a vacuum groove (14) that is connected with a means for production of a negative pressure is incorporated in the face (11).
 15. Tester according to claim 1, characterized in that a thermochuck (23) is provided for the accommodation of pressure sensors (1) located in the wafer compound, in that the wafer (2) is arranged face down on the thermochuck (23) in such a way that the sensor intakes (6) of the pressure sensors (1) arranged in a grid rest directly on the thermochuck (23), in that the thermochuck (23) is provided with a grid of holes (24), and in that the grid of the sensor intakes (6) matches the grid of the holes (24).
 16. Tester according to claim 15, characterized in that the holes (24) are selectively individually connectable with a means for production of a positive pressure or with a means for production of a negative pressure.
 17. Tester according to claim 15, characterized in that the holes (24) are capable of being acted on by pressure, groupwise or linewise, and the holes adjacent to the group or line are capable of being acted on by negative pressure, groupwise or linewise.
 18. Tester according to claim 1, characterized in that a pressure head (15) for production of a flow in the direction of a sensor intake (6) or a sensor element of a pressure sensor (1) for production of a stagnation pressure is provided.
 19. Tester according to claim 18, characterized in that the pressure head (15) is provided with a vertically aligned tubule (16) whose lower opening (17) ends at a specified distance above the pressure sensor (1) and whose other end is connected with a pressure-measuring chamber (18) and a test pressure supply line.
 20. Tester according to claim 17, characterized in that, at the tubule (16) in the region of its lower opening (17), a plurality of needle probes (22) are provided for electrical contacting of the electrical connections (7) of the pressure sensor (1).
 21. Tester according to claim 20, characterized in that the needle probes (22) are capable of being mounted on the electrical connections (7) of the pressure sensor (1) in the elastic region.
 22. Tester according to claims 18 and 19, characterized in that a test card is provided for electrical contacting of each selected pressure sensor (1), and in that a pressure head (15) is positionable on the selected pressure sensor (1) independently of the test card.
 23. Tester according to claims 18 and 19, characterized in that a test card for electrical contacting of each selected pressure sensor (1) is provided, and in that a pressure head (15) is positionable on the selected pressure sensor (1) jointly with the test card.
 24. Tester according to any one of claims 4 to 23, characterized in that the pressure head (9; 15) is fastened to an X-Y-Z cross table. 